1. Field of the Invention
The present invention relates to an audio signal data processing system for processing signal data such as an audio signal data.
2. Description of Background Information
There are known audio signal data processing systems capable of controlling the sound field by which a concert-hall (or theater) acoustics with reverberation sounds and the presence, for example, are created in a listening room or in an automobile. An example of the audio data processing system is disclosed in Japanese Patent Application Laid Open No. P64-72615. In such audio signal processing systems, a DSP (digital signal processor) is provided for controlling the sound field by digitally processing an audio signal output from an audio signal source such as a tuner. The DSP is configured so that operating processes such as operations of the four rules of arithmetic can be repeatedly executed at high speed.
In order to perform the control of sound field precisely, it is necessary to raise the speed of digital processing. However, it has been necessary to use high cost devices for attaining an increased speed of the digital processing. Therefore, reduction of the cost of the DSP has been required.
The DSP is equipped with an operating means for executing operations such as the operations of the four rules of arithmetic, and a data memory for storing the audio signal data to be supplied to the operating means. Furthermore, the DSP is configured so that an external memory for the delaying operation can be connected from the outside for generating a signal delay data by delaying the data stored in the data memory. In the DSP, the structure is such that the signal data is transferred between memories and also from a memory to the operating means in accordance with predetermined programs, in order that the operating process of the signal data can be repeatedly executed at high speed. Such programs are written in a rewritable memory such as the RAM in the DSP, and the program is changed by a microcomputer provided outside the DSP, every time the sound field mode is changed by a manual operation. In other words, variety of sound fields can be created alternately by changing the program.
In the audio signal data processing system described above, there has been the following drawback. When the program is changed, the signal data by the former program remains in the data memory and the delay memory immediately after the change of the program. Therefore, for a certain time interval after the start of the new program the operating process is performed using the signal data before the change of the program. This would lead to generation of improper audio signal data.
Furthermore, a muting function for temporarily stopping the output of the audio signal is generally provided in the audio signal data processing system described above. However, the system is generally structured such that the operating process of the system is stopped during the muting condition, and there has been a problem that a certain time period is required before a proper audio data is actually generated after canceling the muting state.
In the case of the audio signal data processing system described above, it is also desirable that, in addition to the control of sound field by using the DSP, the processing of other functions such as the function of a graphic equalizer can be performed easily.
Furthermore, an A/D converter is generally provided for converting the analog audio signal to a digital audio signal to be supplied to the DSP, in the audio signal data processing system described above. It is necessary that peripheral circuits be provided in addition to the A/D converter in order to attain the synchronization between the sampling timing of the A/D converter and the timing of operation of the DSP. This has been causing a problem in that the number of parts to be added to the DSP from outside becomes large.
The programs mentioned before are normally in the form of a parallel processing program consisting of two series of instructions. By the execution of the parallel processing program, two tasks such as the transfer of the signal data from the delay memory to the data memory and the execution of a certain instruction of arithmetic operation are performed simultaneously in the DSP.
In the case of the parallel processing program, there can be conditions in which the execution of an instruction in one series of processing instructions takes more time than the execution of an instruction in the other series of processing instructions. For example, when the program count value is increased by one, e.g. N, N+1, N+2, . . . , as depicted in FIG. 7, an operating instruction is newly fetched each time the program count value is advanced by one in the first program as the one series of processing instructions mentioned above. In the second program as the other series of operating instructions mentioned above, on the other hand, an operating instruction is fetched each time the program count value is advanced by three, and an instruction NOP that does not specify an operation to be performed is fetched at timings of intervening program count values. In other words, one operating instruction OP in the second program requires an executing time corresponding to steps through which the program count value is advanced by three.
In this parallel processing program, the processing operation by the operating instruction OP of the first program is not subjected to the result of the processing operation by the operating instruction OP of the second program. Therefore, the operating instruction OP is newly fetched each time the program count value is advanced by one in the first program. However, there can be conditions in which the processing operation by the operating instruction OP in the first program is subjected to the result of the processing operation by the operating instruction in the second program. For instance, an operation of transferring the signal delay data from the delay memory to the data memory takes more time than the arithmetic operation. For executing an arithmetic operation after the signal delay data has been transferred to the data memory, the arithmetic operation is subjected to the result of the data transfer operation. In such a case, it is not possible to fetch the operating instruction of the next step when the execution of one operating instruction is completed, as the program count value is incremented. Accordingly, as depicted in FIG. 8, the instruction NOP is also inserted in the first program as in the second program, and the instruction NOP is fetched respectively in the first and second programs until the program count value is increased by two. In this way, the timing is adjusted so that the result of processing operation by the second program is used in the processing operation by the first program.
However, if the instruction NOP is inserted in program as mentioned above, the number of steps of a program increases, so that the program would not be received in the program memory in the DSP, or the efficiency of processing with respect to the capacity of the program memory would be decreased.
Furthermore, the DSP may be provided with a delay time memory for storing a delay time data indicating the time interval between the writing of the signal data into the delay memory and reading of the signal data therefrom. In the DSP, the data are transferred between memories or from memory to the operating means in accordance with predetermined programs, and the processing of the signal data is repeated at high speed as mentioned before. For example, a signal data having been entered is transferred to the delay memory to produce a delay signal data, and the delay signal data is transferred to the operating means via the data memory, and multiplied with a coefficient data. In this way, a reflective sound data is produced in consideration of the level attenuation, to create an acoustic field.
The coefficient data and the delay time data are rewritten by the transfer of new data from the microcomputer outside the DSP each time the sound field mode is switched by a manual operation, so that variety of acoustic fields are created.
However, in such audio signal data processing systems, the number of unit bits of data which can be transferred by the microcomputer is smaller than the number of unit bits of the data controlled by the DSP. As a result, the speed of transferring the coefficient data or the delay time data from the microcomputer to the memory becomes low. Therefore, during the rewriting of data, adequate output of the DSP is not generated for a relatively long interval. Due to this reason, a muting operation for interrupting the output of the DSP, or stopping the processing operation of the DSP has been necessitated. These operations, however, have caused a problem of interrupting the audio output.